Forward Link Only (FLO) is a digital wireless technology that has been developed by an industry-led group of wireless providers. FLO technology uses advances in coding and interleaving to achieve high-quality reception, both for real-time content streaming and other data services. FLO technology can provide robust mobile performance and high capacity without compromising power consumption. The technology also reduces the network cost of delivering multimedia content by dramatically decreasing the number of transmitters needed to be deployed. In addition, FLO technology-based multimedia multicasting compliments wireless operators' cellular network data and voice services, delivering content to the same cellular mobile terminals used in 3G networks.
Today, FLO technology is used to create and broadcast real time multimedia content across various networks to a large number of mobile subscribers. These mobile subscribers generally employ a FLO receiver, which can be described conceptually with a reference model comprising a number of processing layers, typically referred to as a “protocol stack”. Each processing layer includes one or more entities that perform specific functions.
An attractive feature of the protocol stack employed by the FLO receiver is that each layer is self-contained so that the functions performed by one layer can be performed independently of the functions performed by the other layers. This allows improvements to be made to the FLO receiver for one layer without adversely affecting the other layers. However, various challenges are posed when designing the interface between layers in the FLO receiver. Efficient communications across layers in terms of efficient reception of multicast services is always an objective for the FLO receiver designer.
FIG. 1 shows a communications system 100 that creates and broadcasts multimedia content across various networks to a large number of mobile subscribers. The communications system 100 includes any number of content providers 102, a content provider network 104, a broadcast network 106, and a wireless access network 108. The communications system 100 is also shown with a number of devices 110 used by mobile subscribers to receive multimedia content. These devices 110 include a mobile telephone 112, a personal digital assistant (PDA) 114, and a laptop computer 116. The devices 110 illustrate just some of the devices that are suitable for use in the communications systems 100. It should be noted that although three devices are shown in FIG. 1, virtually any number of analogous devices or types of devices are suitable for use in the communications system 100, as would be apparent to those skilled in the art.
The content providers 102 provide content for distribution to mobile subscribers in the communications system 100. The content may include video, audio, multimedia content, clips, real-time and non real-time content, scripts, programs, data or any other type of suitable content. The content providers 102 provide content to the content provider network for wide-area or local-are distribution.
The content provider network 104 comprises any combination of wired and wireless networks that operate to distribute content for delivery to mobile subscribers. In the example illustrated in FIG. 1, the content provider network 104 distributes content through a broadcast network 106. The broadcast network 106 comprises any combination of wired and wireless proprietary networks that are designed to broadcast high quality content. These proprietary networks may be distributed throughout a large geographic region to provide seamless coverage to mobile devices. Typically, the geographic region will be divided into sectors with each sector providing access to wide-area and local-area content.
The content provider network 104 may also include a content server (not shown) for distribution of content through a wireless access network 108. The content server communicates with a base station controller (BSC) (not shown) in the wireless access network 108. The BSC may be used to manage and control any number of base transceiver stations (not explicitly shown) depending on the geographic reach of the wireless access network 108. The base transceiver stations (BTSs) provide access to wide-area and local-area for the various devices 110.
The multimedia content broadcast by the content providers 102 include one or more services. A service is an aggregation of one or more independent data components. Each independent data component of a service is called a flow. By way of example, a cable news service may include three flows: a video flow, an audio flow, and a control flow.
Services are carried over one of more logical channels. In FLO applications, a logical channel is often referred to as a Multicast Logical Channel (MLC). A logical channel may be divided into multiple logical sub-channels. These logical sub-channels are called streams. Each flow is carried in a single stream. The content for a logical channel is transmitted through the various networks in a physical frame. In FLO applications, the physical frame is often referred to as a superframe.
The air interface used to transmit the physical frames to the various devices 110 shown in FIG. 1 may vary depending on the specific application and the overall design constraints. In general, communication systems employing FLO technology utilize Orthogonal Frequency Division Multiplexing (OFDM), which is also utilized by Digital Audio Broadcasting (DAB), Terrestrial Digital Video Broadcasting (DVB-T), and Terrestrial Integrated Services Digital Broadcasting (ISDB-T). OFDM is a multi-carrier modulation technique that effectively partitions the overall system bandwidth into multiple (N) sub-carriers. These sub-carriers, which are also referred to as tones, bins, frequency channels, etc., are spaced apart at precise frequencies to provide orthogonality. Content may be modulated onto the sub-carriers by adjusting each sub-carrier's phase, amplitude or both. Typically, quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) is used, but other modulation schemes may also be used.
FIG. 2 is a conceptual diagram illustrating an example of a protocol stack 200 for the receiver used in one or more of the devices 110 shown in FIG. 1. The protocol stack is shown with a physical layer 202, a Medium Access Control (MAC) layer 204, a stream player 206, a control layer 208, and a number of upper layers 210. The upper layers 210 provide multiple functions including compression of multimedia content and controlling access to the multimedia content. The control layer 208 is used to process control information that facilitates the operation of the device in the communications system. The receiver also uses the control layer to maintain synchronization of its control information with that in the communications system. The stream layer 206 provides for binding of upper layer flows to streams. The stream layer is at the same level as the control layer in the protocol stack 200 of the receiver. The MAC layer 204 provides multiplexing of packets belonging to different media streams associated with the logical channels. The MAC layer 204 defines the procedures used to receive and transmit over the physical layer 202. The physical layer provides the channel structure, frequency, power output modulation and encoding specification for the air interface.
It is well known that the quality of communication over fading channels may be improved by using time diversity techniques. It is therefore desirable to provide for opportunities to improve time diversity.